Radial magnetic bearings having flux paths transverse to the axis of rotation for the rotor are well known in the art. Traditionally, such bearings have one or more actuator cores 10, each of which have constant cross-sectional area magnetic flux paths through the poles 12 and back iron 14 of the core 10, as seen in FIG. 1. The core 10 shown in FIG. 1 is conventionally referred to as an E-core because it is E-shaped with three poles 12 extending from the back iron 14, and a coil 16 wound around each of the three poles. The constant cross-sectional area design allows for the coils 16 to be pre-wound and then slid over the poles 12 in the radial direction during assembly. Additionally, providing a coil 16 on each of the poles 12 serves to increase the magnetic flux through each of the poles and to minimize magnetic flux leakage to the poles 12 on neighboring actuator cores 10.
For such magnetic bearings, the maximum load capacity is determined by the bearing force generated when either the actuator cores 10 or the rotor 18 become magnetically saturated. In the traditional, constant cross-sectional area designs such as shown in FIG. 1, saturation typically occurs either in the back iron 14 or in the area of the coils 16. This is undesirable because the bearing force of such magnetic bearings is proportional to the square of the magnetic flux density in the gap G between the rotor 18 and the tips of the core poles 12. For optimum bearing actuator design, the cores 10 should be magnetically saturated close to the gap G between the tips of the poles 12 and the rotor 18.
There is a continuing desire to improve the load capacity of radial magnetic bearings. Further, there is a desire to provide increased load capacity with little or no increase in the packaging size required for such bearings.